At total body radiation exposures of 3-8 Gy, the predominant cause of death is the hematopoietic syndrome. Many of these deaths are preventable with rapid triage of victims for cytokine therapies and aggressive supportive care. Unfortunately current modalities for identifying patients at risk for the hematopoietic syndrome suffer from inaccuracy, high expense, long analysis times, and delayed diagnosis. Furthermore, none of these methods directly measures radiation damage to the bone marrow, nor do they indicate the existence of residual hematopoiesis, and most are not amenable to point-of-care in emergency conditions. Thus, there is a critical unmet need for a field-deployable diagnostic for use following a radiological incident to identify victims who will develop the potentially fatal ye often treatable hematopoietic syndrome. We propose to build upon a highly successful paradigm in clinical diagnostics, which is that injured tissues leak, shed, and/or secrete proteins into the plasma, where they are useful biomarkers indicating the extent of tissue injury. Precedents include the troponins in myocardial infarction, transaminases in liver injury, creatine kinase in muscle injury, and lipase in pancreatic processes. Accordingly, we hypothesize that following radiation-induced injury to the bone marrow, proteins are released from the marrow into the bloodstream, where they provide useful biomarker signals predictive of the onset and severity of the hematopoietic syndrome. We propose to identify these plasma biomarkers of radiation-induced marrow injury using an innovative approach incorporating targeted proteomic technologies that we have developed and validated in a biomarker discovery pipeline that will substantially increase our chances of success compared with traditional approaches by enabling the testing of a very large (unprecedented) number of plasma biomarker candidates. Aim 1. Using SILAC-labeled mice, identify proteins induced in the bone marrow in response to radiation, and subsequently test hundreds of these putative tissue injury markers to identify the subset that are stably elevated in the plasma post-exposure. Aim 2: Characterize candidate marrow injury biomarkers identified in Aim 1 with respect to their: a. stability in plasma over time, dose range, and dose rates b. correlation with clinical endpoints (indicators of hematopoietic syndrome) c. specificity for damage to the hematopoietic system and damage caused by radiation d. use across a heterogeneous population (pediatric, geriatric, gender, genetically susceptible) Aim 3. Determine which of the radiation biomarkers of marrow damage identified in the mouse are elevated in human blood following radiation exposure, and develop a point-of-care assay device that will form the basis of subsequent human clinical validation trials (beyond this proposal). PUBLIC HEALTH RELEVANCE: History tells us that amidst the immediate panic of a nuclear attack/accident in an urban area, tens-to-hundreds of thousands of panicked people demanding to be evaluated for exposure will likely overwhelm our emergency care system and consequently jeopardize effective triage and treatment of those whose lives are imminently in danger. Additionally, our current tests for determining a specific victim's level of exposure are inadequate to ensure that every victim gets rapid and ideal medical treatment for radiation sickness, which is often survivable if treated rapidly and aggressively. In this proposal, we will develop a field-deployable blood test that will allow us to rapidly determine whether an individual has or has not been exposed to radiation, and if so, what is the best course of treatment to ensure the highest chance of survival.